Radical reactions in vivo--an overview.
Generation of radicals in vivo depends on metabolic activities. The reactions are usually influenced by (i) the presence and concentration of oxygen; (ii) the availability of transition metals (effects of binding and compartimentalization); (iii) the level of reductants and antioxidants (e.g. nutritional effects). The effects of radicals are thought to be due to (i) membrane damage (affecting passive or active transport through altered fluidity/function interrelationships, intercellular messenging through modifications in the synthesis of prostaglandins and leukotrienes); (ii) protein damage (e.g. affecting membrane transporters, channel proteins, receptor or regulatory proteins, immunomodulators); (iii) damage to DNA. Defense mechanisms consist of (i) prevention of the 'spreading' of primary damage by low molecular weight antioxidants (e.g. vitamin E, GSH, vitamin C, beta-carotene, uric acid); (ii) prevention or limitation of 'secondary' damage by enzymes (e.g. GSH-peroxidase, catalase, superoxide dismutase, DT-diaphorase) and/or chelators; (iii) repair processes, e.g. lipid degradation/membrane repair enzymes (phospholipases, peroxidases, some transferases and reductases), protein disposal or repair enzymes (proteases, GSSG-reductase), DNA degradation repair enzymes (exonuclease III, endonucleases III and IV, glycosylases, polymerases). Recent hypotheses on a messenging function of the superoxide anion O2- are discussed and possible implications of cross-reactions between O2- and nitric oxide (endothelium-derived relaxing factor EDRF) are shortly mentioned.
Saran
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M
GSF-Institut für Strahlenbiologie, Neuherberg, Federal Republic of Germany.
Bors
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W
D000975:Antioxidants / Q000378:metabolism; D002384:Catalysis; D003600:Cytosol / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004249:DNA Damage / Q000502:physiology; D005110:Extracellular Space / Q000378:metabolism; D005609:Free Radicals; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D008566:Membranes / Q000378:metabolism; D008670:Metals / Q000378:metabolism; D011506:Proteins / Q000378:metabolism
D000975:Antioxidants; D005609:Free Radicals; D008670:Metals; D011506:Proteins; D004247:DNA